To estimate a maximum purchase price for the coin in question, we can consider several factors:

1. Current Condition: The coin has a condition of 80 (MS+), which indicates that it is in quite good shape. This generally translates to a higher price compared to coins with lower conditions.

2. Auction History:
- The average hammer price in previous auctions is 69.02 euros.
- The last auction for this coin had a hammer price of 65 euros with a condition of 80.
- In previous auctions, hammer prices have varied, but there are examples of hammer prices exceeding 200 euros for coins of similar or better condition.

3. Starting Price and Average Starting Price:
- The current starting price is 20 euros, which is relatively low compared to the average starting price of 35.64 euros.

4. Sales Trends: The coin has been auctioned 15 times, of which 9 have been sold. This indicates a consistent interest in the coin, which may influence its price.

Based on these factors, an estimated maximum purchase price could be in the range of 80 to 100 euros, considering that the condition is good and that the auction price history suggests it could reach higher figures in auctions. However, since the starting price is low, it could be a good opportunity to acquire it at a reasonable price.